ABSTRACT Cardiovascular disease, the leading cause of death worldwide, has pathologic etiology underscored by the dysregulation of blood pressure. One potent system for regulating blood pressure homeostasis is the production of nitric oxide (NO) by NO synthase enzymes in resistance arteries. Under physiologic conditions, endothelial cells generate gaseous NO by activating endothelial NO synthase (eNOS). Consequently, NO diffuses to underlying smooth muscle cells to activate soluble guanylyl cyclase/cGMP-dependent pathways and induce vasodilation. Thus, dysfunction of NO-mediated signaling can lead to reduced vasodilation and increased blood pressure. Recently, the alpha chain of hemoglobin (i.e., alpha globin) has emerged as a novel regulator of NO signaling in the blood vessel wall. In addition to its established role as a gas binding protein, work from the Isakson and Columbus labs have shown that endothelial-derived alpha globin can limit diffusible NO availability and control vasodilatory signals. Moreover, the localization of eNOS and alpha globin to the myoendothelial junction (MEJ), a projection of endothelial cells that directly contacts smooth muscle cells for cell to cell communication, morphologically supports a regulatory role for alpha globin during vasodilation. We have also shown that alpha globin and eNOS form a macromolecular complex, which directly interact to influence NO availability. A 10- residue peptide mimicking a highly-conserved region in alpha globin (35LSFPTTKTYF44, called Hb?X) is sufficient to disrupt alpha globin/eNOS complex formation in vitro2. Additionally, Hb?X has powerful blood pressure lowering effects at baseline and in a model of systemic hypertension. One vasoconstrictive pathology associated with endothelial dysfunction and decreased NO signaling is pulmonary hypertension (PH). Elevation of pulmonary blood pressure increases load on the right ventricle, leading to death in about 3 years. A therapeutic approach that aims to increase a powerful vasodilatory signal (as is eNOS/NO signaling) is a valuable goal. Current pharmacological approaches include inhaled NO as an emergency therapy for increased pulmonary pressure, highlighting disruption of the alpha globin/eNOS complex to increase NO as a possible target for treatment of PH. This proposal is focused on how an alpha globin mimetic peptide disrupts the alpha globin eNOS complex. Biophysical characterization of the alpha globin/eNOS complex will be accomplished with studies of the binding interface of the Hb?X peptide with eNOS and extended to full protein. Additionally, a role for increased NO signaling as a treatment for pulmonary hypertension is proposed. A dual approach, using pharmacologic treatment (by peptide injection) and a genetic mouse model we have developed will be used to determine the efficacy of increased NO in pulmonary vasoconstrictive disorders.